This invention relates to release agents, toner particulates and toner compositions. This invention also relates to methods of improving dry fuser release for the prevention of fuser jamming and fuser wrapping, and of methods of improving overhead projection transparencies.
Numerous methods and apparatuses for electrophotography, electrostatic recording and electrostatic printing are known in the art. Typically, a charged photosensitive surface, for example a charged photosensitive drum, is irradiated with an optical image and an electrostatic latent image is formed on the photosensitive surface. In the development process, a developing agent, i.e., toner, is adhered to the electrostatic latent image.
Typically, toner is fed to a developer roller by a metering blade positioned against the surface of the developing roller. The developer roller, with the toner on its surface, is typically rotated in a direction opposite to that of the photosensitive drum (or in the same direction at a different speed), and toner adheres to the electrostatic latent image to develop the image. Various toner compositions have been developed in order to provide improved copying, recording and/or printing with such apparatus.
One method of fusing a toner image to a substrate is to bring the toner in contact with a hot surface such as a heated roller. However, there is a tendency for a fuser to collect small amounts of toner which in turn causes toner offset to build up on the fuser surface. This toner may be then transferred to a subsequent substrate, thereby causing a poor image.
The fuser roll surface may be wetted with a release agent such as a silicone oil in order to decrease the problem of toner offset. Unfortunately, the silicone oil release agent may leave oil residues on the paper, thereby interfering with the image quality. Additionally, the release agent material tends to migrate to other surfaces within the printer where it interferes with proper development of the latent image to diminish print quality, especially in the case of duplex printing. Therefore, a dry fuser, that is a fuser without any oil on its surface, is often desirable.
In order to solve the problem of toner offset with dry fusers, lubricants or waxes are often added to the toner. Unfortunately, at high concentrations effective for the purpose of dry fuser release many conventional lubricants tend to separate from the toner during the process of development, and stick to the doctor blade causing a filming problem which adversely affects print quality.
Toner release from dry fusers has been enhanced by modification of toner resin rheology. High molecular weight resins or resins having crosslinks may exhibit improved release. Unfortunately, use of such high molecular weight or crosslinked resins generally results in poor clarity of overhead projection transparencies or in inadequate fuse grade at higher speeds. Generally, high transparency or excellent high speed fuse grade requires lower melt temperature resins or higher fusing temperatures, but such resins or temperatures cause toners to adhere easily to dry fuser rollers. Thus, it is difficult to develop toners for transparencies or lower temperature fusing applications which exhibit good release, good fuse grade and the good transparency needed for reproduction of a large color gamut and for clarity. Generally, in order to maintain good clarity and high speed fuse grade, the lower melt temperature resins used in toners require that a separate release agent be used.
Tomita et al., U.S. Pat. No. 5,225,303, disclose a toner comprising binder resin, coloring agent, and a release agent, which contains as the main components a carnauba wax substantially free of aliphatic acids and/or a montan ester wax, and an oxidized rice wax with an acid value of 10 to 30. Tomita et al. teach that the acid value of the montan ester wax is preferably in the range of from 5 to 14, and that the carnauba wax preferably comprises 5 weight percent or less free aliphatic acids.
Inoue et al., U.S. Pat. No. 5,643,705, disclose a toner comprising a toner particulate containing a polyolefin wax and a modified polyolefin wax. Inoue et al. disclose the polyolefin wax is a low number-average molecular weight polyethylene or low number-average molecular weight polypropylene having a softening point of from 80xc2x0 C. to 160xc2x0 C., and that the modified polyolefin wax is mainly composed of low number-average molecular weight polyethylene, wherein the modifying component used to modify the polyolefin wax is an aromatic vinyl monomer, an acrylate monomer, an unsaturated dicarboxylic acid ester or a mixture thereof.
Taguchi et al., U.S. Pat. No. 5,466,555, disclose a releasing composition comprising 60 to 99.5% by weight of a low molecular weight polypropylene having a melt viscosity of 15 to 2,000 cps at 160xc2x0 C., and 0.5 to 40% by weight of at least one modified polyolefin selected from the group consisting of low molecular weight polypropylene having a melt viscosity at 160xc2x0 C. higher than that of the first polypropylene, modified with an ethylenically unsaturated carboxylic acid or an anhydride thereof, and a modified polyethylene comprising a low molecular weight polypropylene having a melt viscosity of 10 to about 8,000 cps at 1 40xc2x0 C., modified with an ethylenically unsaturated carboxylic acid or an anhydride thereof.
Katada et al., U.S. Pat. No. 5,972,553, disclose a toner comprising polymer components, a colorant, a charge control agent, and a wax terminally modified with at least one of maleic acid, maleic acid half ester, or maleic anhydride. Katada et al. teach that the polymer components include a low molecular weight polymer component having an acid value Avl and a high molecular weight polymer component having an acid value Avh such that Avl is greater than Avh. Katada et al. further teach that the wax has an acid value Avwax satisfying Avl greater than Avwax, and Avwax greater than 0 mg KOH/g, and that the wax may have an acid value of 1 to 15.
Unfortunately, many prior art toner compositions comprise large amounts of release agents such as waxes, and such large amounts tend to interfere with print quality. Other prior art toners comprising waxes have a poor fuse grade, that is, the print is not resistant to abrasion and may be abraded or scraped off. Some waxes, such as polyolefin waxes, tend to migrate to the photoreceptor causing poor print quality, or causing staining of the photoreceptors. Further, many color toners which contain release agents fail to exhibit both good release and the good transparency needed for reproduction of a large color gamut and for clarity.
In the pursuit of high quality, vibrantly colored overhead transparencies, it has been discovered that the achievement of this goal through electrophotography is dependent not only upon the inherent transparency of the binder resin, but upon the release/transparency (r/t) window of said binder resin. The r/t window of a toner is defined as that range of temperatures in which a toner is sufficiently fused to produce a bright, colorful image when projected and where it releases cleanly from the fuser hot roll. This window is the cross section of the independent release and transparency windows. Each resin system has its own characteristic cross section. xe2x80x9cReleasexe2x80x9d refers to the tendency of a developed image to wrap the fuser roll upon nip exit at a given temperature. The release window is a range of temperatures bounded at the low end by cold offset and at the high end by fuser adhesion or hot offset. xe2x80x9cTransparencyxe2x80x9d refers to the ability of a toner to transmit light without scatter. The transparency window can be measured by evaluating the percentage transmitted light through a sample that has been fused at a given temperature. It is a range of temperatures bounded by low fuse grade, characterized by muddy projected color, and hot offset, where the rough toner surface begins to scatter light. The overlap of the release range and the transparency range of a given toner at a specific mass per unit area is the release/transparency window for that toner.
It is desirable that the r/t window be wide and achievable at temperatures sustainable for the lifetime of a fuser assembly. Typically the range of temperatures where a binder resin achieves transparency corresponds to the onset of fuser wrapping. The properties that lead to excellent transparency, low molecular weight, low melt temperatures, low viscosity, and low gel content, also generally yield poor wrapping, filming, and hot offset performance.
These principles of release may also be applied to black toners. The market trend is not merely to color toner but also toward higher speed printing. Though obviously lacking any requirement for the achievement of transparency, like requirements for the projection of color, high speed fusing requires toners with rapid melting characteristics. Black toners must achieve adequate fuse grade, sufficient melting of the toner powder to cause tenacious adhesion of the toner image to the substrate. Black toners may be said to have a release/fuse grade window analogous to the release/transparency window defined above for color toners. Like with the color example, the properties that support rapid fusing, low molecular weight, low melt temperatures, low viscosity, and low gel content, generally yield poor wrapping, filming, and hot offset performance.
High molecular weight resins may release effectively but cannot achieve a satisfactory transparency or fuse grade at temperatures that can be maintained without damage to the fuser assembly. Crosslinked resins may contain sufficient elasticity to release at a wide range of temperatures, but are likely to be characterized by low fuse grade. The balance of release and transparency/fuse grade is difficult to achieve with resin chemistry alone. Conventional solutions to this challenge include the incorporation of release agents, such as polypropylene waxes, into the toner formula, or the application of low melt release agents, such as silicone oil, to the surface of the hot roll. Chemically polymerized toners using high levels of encapsulated wax have also appeared. Though these methods are each utilized in the industry each has its own disadvantages.
The level of internal release agent required for adequate release in low melt systems is generally high, forming large domains of incompatible material, and therefore usually accompanied by a strong tendency to film the electrophotographic (EP) components. This filming leads to the destruction of image quality. Higher levels of internal wax in conventional toner can be achieved through the use of compatibilizing agents, but these agents tend to decrease the effectiveness of the wax and also have a negative effect on transparency. Chemically prepared toners (CPTs) with high levels of encapsulated wax suffer from haze. Though use of an oiled hot roll avoids the occurrence of filming and the appearance of haze, the oil has a tendency to migrate. This migration of oil results in the disruption of the duplexing capability of the machine. Metering mechanisms have been designed to limit the amount of oil flowing through the system at any given time. These metering devices, however, are expensive and dramatically increase the price of a printer.
Thus, there is a need for methods of improving toner release which produce high image quality overhead transparencies with vibrant projected color. Particularly, there is a need for methods of improving or enhancing toner release which avoids the need for expensive metering mechanisms. Further, there is a need for release agents which may be incorporated into toner particles thereby providing toner compositions with adequate fuse grade and good dry fuser roller release, and which provide good print quality and acceptable clarity for overhead projection transparencies. The release agent should not promote smearing or blocking of toner, or filming on the doctoring blade, developer roller or the photoconductor drum.
Accordingly, an object of this invention is to provide improved release agents, toner particulates and toner compositions.
It is another object of this invention to provide methods for improving dry fuser roller release.
It is a further object of this invention to provide methods of improving color clarity in overhead projection transparencies.
It is yet another object of this invention to provide toner compositions having adequate fuse grade.
It is yet another object of this invention to avoid component contamination by residual oil by using an oil-free dry fuser roller and toners which release from the dry fuser roller without filming.
It is yet another object of the invention to provide toner compositions exhibiting good dry fuser roller release.
In accordance with one aspect of the invention there are provided release agents comprising, by weight, no more than about 50% wax and at least about 50% functionalized enhancing agent, while in accordance with another aspect of the invention there are provided release agents comprising from about 15% to about 75%, by weight, wax and from about 25% to about 85%, by weight, functionalized enhancing agent. The wax has a number-average molecular weight of no greater than about 10,000.
In accordance with one aspect of the invention there are provided toner particulate comprising a release agent comprising wax and functionalized enhancing agent; wherein the release agent comprises, by weight of total release component, no more than about 50% wax and at least about 50% functionalized enhancing agent, while in accordance with another aspect of the invention there are provided toner particulates comprising a toner binder resin, a colorant, a charge controlling additive and a release agent, wherein the release agent comprises from about 15% to about 75%, by weight, wax and from about 25% to 85%, by weight, functionalized enhancing agent. The wax has a number-average molecular weight of at no greater than about 10,000.
In accordance with one aspect of the invention there are provided methods of improving the release/transparency window of an overhead projection substrate of a color toner image using a low oil or oil-less fuser roll comprising the step of printing the overhead projection substrate with a composition comprising toner particulates, wherein the toner particulates comprise a colorant, resin and a release agent comprising, by weight of total release agent, no more than about 50% of a wax having an acid value of no more than about 10 and a number-average molecular weight of at no greater than about 10,000, and at least about 50% of a functionalized enhancing agent having an acid value of from about 10 to about 100.
In accordance with yet another aspect of the invention there are provided methods of improving dry fuser release of a toner composition, comprising the step of providing the toner composition with a release agent, wherein the release agent comprises, by weight, no more than about 45% wax and at least about 55% functionalized enhancing agent.
In accordance with yet another aspect of the invention there are provided toner compositions comprising a wax, and a functionalized enhancing agent comprising a polyalkylene having at least one maleic half ester moiety grafted onto the polyalkylene.
Additional embodiments and advantages of the toner compositions, toner particulates, release agents and methods herein will be apparent from the following description.